The glass industry has utilized air-fuel burners to melt glass and glassy like materials over the years. The developed processes included the use of submerged air-fuel combustion burners. These burners were located in the bottom or side wall of the furnace below the melt line. The advantages looked for in submerged combustion were increased heat transfer from the flame and the avoidance of high flame temperatures on the crown of the furnace.
In operation, the high volumes of air-gas resulted in open tunnels or chimneys up through the glass. The unstable nature of these "chimneys" resulted in their partial collapse or blockage with molten glass. The high volume of combustion gases from the vertical bottom entering burners and the parallel side entering burners result in rapid expulsion of gobs of glass in all directions. Some additional disadvantages observed included difficult maintenance of the burners, splashing of the glass over the crown with subsequent attack, a dirty off gas stream, difficult recuperation, and a very noisy operation.
While these early attempts focused on the flame temperature-heat transfer opportunity, they apparently failed to take into account the local effects of the heat transfer and the rather high kinetic energy of the flame and its transfer to the glass on the refractory structure and the fluid flow pattern of the melt volume. These localized effects resulted in very hot refractories adjacent to the burners as well as significant "washing-out" of the refractories due to the high velocity of the glass in this same area. Some of those disadvantages result from using stationary burners in the vertical position. In the bottom location, the high kinetic energy of the combustion stream results in ejection of glass at high velocity all over the furnace crown.
In the prior art process, all of the required melting heat was supplied through the submerged burners.